Management of flowback and produced (F/P) water from conventional and unconventional oil and gas wells has been deemed by the US Department of Energy as the largest volume waste stream associated with oil and gas production. With increased oil and gas production from unconventional resources F/P water management is a growing concern worldwide. In 2007, oil and gas fields produced over 80 billion barrels of water requiring processing. Global cost estimates stemming from F/P water management are more than $40 billion annually, with water transportation costs accounting for an additional $20 billion annually.
Within North America, tremendous growth in oil and gas production has been realized through the development of unconventional shale reservoirs. Two significant obstacles to continued unconventional shale development are the availability of water for drilling and hydrofracturing and management of F/P water from unconventional wells. During development of a horizontal well, 1 to 6 million gallons of fresh water may be used to stimulate the shale formation. The fracturing fluid is typically composed of approximately 90.6 wt % water, 9.0 wt % proppant, and 0.4 wt % of additives. Up to 750 chemicals have been used as additives for fracturing fluid and consist of acids, biocides, breakers, clay stabilizers, corrosion inhibitors, crosslinkers, friction reducers, gelling agents, iron control, pH control, scale inhibitors, and surfactants. After fracturing over 1 million gallons of F/P water is generated from each well which must be transported offsite for proper disposal.
F/P water contains a variety of components from both the fracturing fluid and shale formation. Table 1 presents a summary of some of the components and concentration ranges found in F/P water. The compositions of F/P water are quite different and both can vary with time and location. In general, flowback water typically contains higher hydrocarbon and chemical compositions due to its fracturing fluid content, while produced water contains higher total dissolved solids (TDS) from the shale formation. Hydrocarbons and chemicals found in F/P water are both polar and non-polar in nature, while typical dissolved solids constituents include Al, Ba, Ca, Fe, Li, Mg, Mn, Na, and Sr in the form of chlorides, carbonates, and sulfates. Additional F/P water components includes suspended solids, bacteria, and normally occurring radioactive material.
TABLE 1Key Flowback and Produced Water ContaminantsConcentrationConstituent (mg/L)Ba2,300-6,500Ca 5,100-18,000Fe11-60Mg 4440-1,300Mn2-5TDS 69,000-300,000Hydrocarbon  40-1,000TSS 100-500
Conventional F/P water disposal currently used by the gas industry consists of separating F/P water from proppant and gas, followed by interim flowback water storage. The flowback water is then transported to a disposal pit, evaporation pond, or recycling facility offsite. A more attractive fluid management option is to reuse F/P water in subsequent drilling activities. However, F/P water cannot simply be reused due to its host of components which can interfere with subsequent hydrofracturing activities.
The present invention provides a cost-effective F/P water treatment process for onsite operation allowing water to remain within the field reducing water demand and need to transport F/P water offsite.